Thailand for 7 days

With 7 days to burn you can get to almost any beach in Thailand and enjoy it for a spell. Give Pattaya a miss - too sleezy, dirty, and loud. The closest good beaches are on Ko Samet, about 4 hours from Bangkok by bus/van/boat and easy to arriange the day before or even same day if you try. You'll want to keep an eye on current weather conditions wherever you go, as rainy season is on the way in now in many areas. However, as has been said a million times already here, tropical rains are seldom all day and usually strong and short, so you should find some good sun just about anywhere. Might be a sound idea to head down to Ko Phangan and stay on Thong Nai Pan Yai or Bottle Beach. Something even quieter head down the west coast to Ranong and get a boat to Ko Payam (very basic) but again have a look at the current weather west vs. east coasts when you arrive and stab from there. Thi sort of "best beach in Thailand" thing comes up almost daily and you'd have to coerce some folks to give up theri best kept secrets so don't hold your breath. Good Luck.

My personal favourite has to be "The Beach" itself, (the one they used for the film of the same name). It's on Phi Phi Ley island and it's called Maya Bay. It's completely breathtaking. To get there you'll need to go to Phi Phi Don which is the larger (i.e. inhabited) island and then get a local from one of the hundreds along the shore to take you to Maya Bay. It should cost about £5 for the boat (i.e. up to about 4 people) for about 3 hours and includes snorkelling equipment. The snorkelling is awesome too, take some bread or bananas with you and the fish go mad! I'm so jealous, enjoy!

The best beach I experiences was on Koh Change (the one near the Cambodian border), postcard perfect.

Try the krabi area , then ao nang, beautiful with lots of longtails to take you to many islands that are private or snorkling, for a 1.00 - 2.00 dollars.
very cheap go back to ao nang for lodging great sun sets. then can take big boat to the BEACH island, phi phi. for few dollars all beautiful.

Listen this is the year 2007. The BEST beaches in Thailand are all tourist traps! No fault of your own but you're r 20 years too late if you're looking for undiscovered Thailand. If you truley are looking for the best undiscovered and tourist free, for the moment, or at least less so than Thailand, then go to North Vietnam up or the west coast of cambodia otherwise join the crowds. I agree Krabi is beautiful and I love hiring the long tails for days of island hoping but then again everybody goes there, there are tons of tourists and the beach bungalows are a distant memory. :< Don't want to rain on your parade but..be realistic....

When are you travelling? That makes a fair difference to which beaches will be nicest. Plenty of unspoiled beaches left.

in November.
How is Ko Samui

Um, well November is just about Samui's wettest month. You can still have a nice holiday there and get lots of sun (my one Nov trip to Samui I did just that), but anedotally, the most complaining posts I've seen about sustained rain/overcast have come from the southern Gulf in Oct/Nov/Dec. See first link below for more details.
Samui is nice enough, but today is more geared for the midrange and upper traveller - flash hotels, beach deck chairs, theme pubs, girlie bars, Maccas etc. You can still find budget bungalows and quieter beaches, but other islands are a better bet if you are seeking this.

Visually a must visit beach is West Railay (and nearby Phra Nang), but I wouldn't call it unspoiled. In November you should beat the crowds. Weather is usually better Andaman side in November. November is probably my favourite time to travel the Andaman.

So what is unspoiled? If you mean totally deserted there are a few on Ko Jum, several on Ko Yao Noi, two on Ko Kradan, lots on Taratao.

If you mean just a few bungalows, maybe a restaurant there are heaps - Jum, Yao Noi, Kradan, Ngai, south end of Lanta, Ko Phayam, little Ko Chang Andaman side, Ko Libong, Ko Lipe, Ko Bulon Lae to mention a few.
I have info on all of these except Tarato and Bulon Lae in the second link below.

Samui is vile!!! Dont go there!